So-called selectorized weight machines have been used in fitness clubs and athletic training facilities for many years. These machines allow the user to select the amount of weights on a weight stack which will be lifted during the exercise or training protocol.
A specialized version of a selectorized weight machine is one which allows for variable resistance along the range of motion of the exercise or training protocol. These selectorized variable-resistance weight machines utilize a cam having a varying radius or cam profile. Cable means of some kind, such as an actual wire cable, a chain, a belt or the like, is attached at one end to a weight stack and is attached at the other end to the cam. When the user rotates an input assembly fixed to the cam, the cam rotates and winds up the cable, chain, etc., thereby lifting the weights from the weight stack. The changing cam profile varies the mechanical advantage of the weights which the user encounters. The cam profile is designed to approximate the change in anatomical mechanical advantage of the user at each point in the range of motion.
Ideally, when the user is at a "weak" point in his or her range of motion, i.e., when the user is at an anatomical point in the range of motion where the user is unable to lift much weight, the cam profile will match this weakness by minimizing the mechanical advantage which the weight stack has on the user.
Similarly, the cam profile is designed to modify the mechanical advantage of the weight stack in an appropriate fashion when the user is at a "strong" point in the anatomical range of motion. In this case, the cam profile will maximize the mechanical advantage which the weight stack has on the user.
The varying radius of the cam profile is an attempt to approximate an ideal situation where the user is lifting as much weight as he or she can at each point in the user's range of motion.
The "selectorized" aspect of selectorized variable-resistance weight machines allows the user to select varying number of weight plates from the weight stack. This is usually accomplished by inserting a pin into one of the plates.
Selectorized variable-resistance weight machines are well known in the industry, for example, those prior models made by EAGLE.RTM. Fitness Systems by Cybex (an unincorporated operating division of the assignee of the present application) and Nautilus Sports Medical Co.
Selectorized variable-resistance weight machines are also used in the rehabilitation field, as well as for exercise and training. For rehabilitation purposes, it is often important to limit the range of motion the patient is allowed to go through on the machine during the rehabilitation protocol. For example, after certain knee injuries, it is important that the patient avoid loading muscles with weights at certain points in the range of motion for knee extension. However, for other points in the range of motion for knee extension, use of a weight machine may play an important part in the rehabilitation protocol.
Selection of an appropriate start and stop point in the range of motion can be critical in the rehabilitation setting. Injury may result if the patient loads his or her limb with weights from the weight stack at an undesired position in the range of motion. Sports medicine and rehabilitation physicians and physical therapists have long recognized that there are certain safe ranges of motion for rehabilitation of particular injuries, and that use of selectorized variable-resistance weight machines outside of those ranges can be dangerous to the patient.
In the exercise and training fields, there are also advantages to narrowing the allowed range of motion in weight training. For example, athletes sometimes concentrate on developing muscle strength and bulk over limited specified, ranges of motion.
Prior art means for limiting the range of motion on selectorized variable-resistance weight machines have generally fallen into two categories. In both categories, the stop or end position for the range of motion is accomplished by adjusting the location of a stop pin or a block such that the input assembly or rotating member of the machine hits the pin or block at the desired stop point in the range of motion.
The difference between the two categories of prior-art machines relates to the manner in which the start position for the desired range of motion is accomplished.
In the first category, the user, clinician or therapist rotates the input assembly or rotating member of the machine to the desired start location, thereby also lifting the weights. The user, clinician, etc. inserts a mechanical stop against which the input assembly or rotating member rests.
This first category of machines has the obvious disadvantage that the weight stack must be lifted in order to make the adjustment, and a mechanical stop must be put in place after each adjustment is made.
The second category of machines disconnects the input assembly or rotating member from the weight stack and cam before the adjustment of the start position is made. This is done, for example, by use of a clutch or pull pin. This has major disadvantages when used with a variable-resistance weight machine. Once the input assembly or rotating member is reoriented with respect to the cam on a variable-resistance machine, the changes in the anatomical mechanical advantage of the user and the changes in the cam mechanical advantage are no longer synchronized. Depending on the particular exercise, training or rehabilitation protocol (e.g., leg curl, arm curl, shoulder press, etc.) the maximum cam effect could occur at the user's weakest point of anatomical advantage, resulting in a risk of injury to the user.
There remains a need on variable-resistance weight machines for a range-limiter device which does not require that the weight stack be lifted to make a start-position adjustment nor requires reconfiguring the relationship between the anatomical mechanical advantage of the user and the cam profile to make such an adjustment.